RT Journal Article SR Electronic T1 Effect of Position on Dural Puncture During Epidural Needle Placement in Patients with Previous Back Surgery JF Regional Anesthesia: The Journal of Neural Blockade in Obstetrics, Surgery, & Pain Control JO Reg Anesth Pain Med FD BMJ Publishing Group Ltd SP 115 OP 115 DO 10.1136/rapm-00115550-199722021-00115 VO 22 IS Suppl 2 A1 William Ackerman YR 1997 UL http://rapm.bmj.com/content/22/Suppl_2/115.abstract AB